1. Field of the Present Invention
The present invention relates generally to apparatus used in dentistry, and more particularly to a dental articulator for simulating the movement of upper and lower dental prostheses within the normal range of movement of a particular condylar construction.
2. Description of the Prior Art
A dental articulator is a form of jig employed in prosthodontics to assure that the dental prostheses are accurately configured to permit mating of the occlusal surfaces and unobstructed, comfortable displacement of the prostheses when secured to the jaw structures of the patient. Generally, the previously known articulators comprise an upper arm adapted to support an upper dental cast including prostheses which is slidably, displaceably secured to a base adapted to support a lower dental cast including prostheses. The means for displaceably securing the upper arm to the base generally comprises an adjustable displacement hinge mechanism which permits relative movement between the arm and the base, and thus between the dental casts, to approximately simulate relative movement between the upper and lower prostheses which would normally occur in the mouth by means of the condylar joint connecting the mandible to the maxillary structure of the patient's head. Typically, the inclination of the displacement in the hinge means is adjustable so that actual differences between various condylar structures can be approximately replicated by a single articulator. One of these previously known articulators is disclosed in U.S. Pat. No. 4,304,551 to Kowasaki.
The disadvantage of the previously known articulators is that the hinge means, or condylar guidance mechanism, provides movement which is similar to, but not accurately representative of, the movement caused by an individual's condylar joint. Thus, while the articulators are of some benefit in aligning and fitting dental casts so that displacement along their occlusal surfaces occurs without obstruction, substantial work may still be necessary upon the prostheses once they are installed in the patient's mouth to accomodate the actual movement caused by the patient's condylar joint. Moreover, the articulators are complex structures and due to the complexity of the parts, especially the condylar guidance hinge, are therefore quite expensive to produce and purchase.
One previously known method for increasing the accuracy of simulated condylar movement of the dental impression is to record a graph of the actual movement produced by a patient's condylar movement and aligning the condylar hinge of the articulator in accordance with the graph record produced. Nevertheless, once the general slope of condylar movement has been determined, the articulator only approximates actual movement since the line of displacement in the articulator, such as the articulator disclosed in U.S. Pat. No. 4,304,551, is restricted to a linear displacement regardless of the actual, varying slope to which movement is adjusted.
Moreover, the making of the graph is a rather complicated procedure. A writing stylus is secured to an upper face bow, a frame structure adapted to be fixedly secured to the maxillary structure of a patient's head. A graph plate upon which the stylus writes is secured to a lower face bow, a frame structure adapted to be fixedly secured to the mandibular structure of the patient. The stylus and graph plate are positioned so as to be in registration with one another so that movement of the mandible with respect to the maxillary structure permits the stylus to imprint a graphic representation of the movement on the graph plate. Such structure is also rather complex and expensive due to the mechanisms which are necessary to securely fit the face bow to the patient.
Another previously known improvement which permits the articulator to more closely simulate the actual movement of a particular condylar structure comprises a use of an impression stylus fixedly secured with respect to the maxillary structure, which forms an impression in impressionable material fixed with respect to the mandibular structure. Such an impression forms a more accurate record of the movement of the patient's jaw. Such impressions can be formed within the oral cavity, or exteriorly of the oral cavity, but in either case, it is typically formed at a position away from the condylar axis so that the impression, or a cam guide surface formed from the impression, can be mounted on the previously known articulator. The impression, or cam guide surface, is then used to control the operation of the condylar hinge means of the articulator for example, by means of an incisal pin which rides in the cam guide surface, and operates in conjunction with the condylar hinge means.
Nevertheless, the complex and time consuming procedure of forming the impression is quite similar to the procedure outlined above with respect to the graphic recording of condylar joint movement. Moreover, incorporation of the impression in the articulator further increases the cost and complexity of the dental articulator. Moreover, even though the condylar hinge means can be made mechanically responsive to the guiding surface of the impression material incorporated in the articulator, maladjustment of the hinge means or limitations in its range of movement can interfere with accurate displacement of the upper and lower dental impressions despite the accuracy of the movement impression made during the actual movement of the patient's jaw.